In the field of sludge disposal, sludge concentration processing and sludge dehydration processing are performed. At this time, processing for adding a flocculant and flocculating sludge is performed in order to improve sludge concentration efficiency and sludge dehydration efficiency. In the field of water treatment, processing for flocculating and precipitating suspended substances is performed. Also, at this time, processing for adding a flocculant to water to be treated and flocculating suspended substances is performed in order to improve the efficiency of flocculation and precipitation.
In the above-described sludge disposal and water treatment, various flocculants such as an inorganic flocculant, a cationic polymer flocculant, and an anionic polymer flocculant are used selectively. Of these flocculants, solid polymer flocculants have the drawback of being poorly soluble in a liquid while exhibiting a high flocculation effect due to cross-linking flocculation. Therefore, solid polymer flocculants are not added directly to sludge or the like, but are dissolved in water in advance to form an aqueous solution and then added to sludge or the like such that a predetermined chemical injection rate is achieved.
However, the polymer flocculants have another problem in that, if a long period of time passes after an aqueous solution of the polymer flocculant has been prepared, the aqueous solution deteriorates, resulting in a decrease in the flocculation effect. Therefore, it is not preferable that a large amount of the aqueous solution is prepared in advance and stored in a tank or the like. In order to sufficiently achieve the original flocculation effect of the polymer flocculant, it is preferable to add a fresh aqueous solution that is used as soon as possible after the polymer flocculant has dissolved in water.
However, when the dissolving time is short, a problem arises in that the polymer flocculant remains undissolved. When being added to sludge or the like, the undissolved polymer flocculant does not immediately exert the flocculation action. Therefore, even in conventional techniques, a dissolving method with which the amount of an undissolved polymer flocculant is reduced to a minimum, and the additional arrangement of an apparatus for dissolving the undissolved polymer flocculant have also been investigated (see Patent Documents 1 to 6, for example).
Patent Document 1 discloses a technique for crushing an undissolved polymer flocculant using a tubular mesh filter and a roller that rotates in the filter and dissolving the undissolved polymer in water. Patent Documents 2 and 3 also disclose techniques for crushing an undissolved polymer flocculant and dissolving the undissolved polymer flocculant in water. Patent Document 4 discloses a technique for grinding an undissolved polymer flocculant using a colloid mill and dissolving the undissolved polymer flocculant in water. Patent Documents 5 and 6 also disclose techniques for grinding an undissolved polymer flocculant and dissolving the undissolved polymer flocculant in water. Regarding the technique for grinding an undissolved polymer flocculant, use of a fixed disk and a rotary disk has also been investigated. It is thought that, with the techniques disclosed in Patent Document 1 to 6, a polymer flocculant can be dissolved in a short period of time, but power required for grinding an undissolved polymer flocculant mechanically is by no means low. Furthermore, there is also a concern that the action of crushing a polymer flocculant mechanically will cause the breakage of the molecular structure of the polymer flocculant, resulting in deterioration of the flocculation action.